1. Field of the Invention
The present invention relates to a time-division color projection type display apparatus.
2. Description of the Related Art
Conventionally, there has been proposed a time-division color projection type display apparatus which is basically configured to project images of a plurality of different colored light rays including a plurality of different colors, for example, red, green, blue, or white in a time division mode to display a color image for display. For example, Japanese Patent Laid-Open Publication No. 78550/98 discloses a DMD projector which utilizes an image display device that comprises a digital mirror device (hereinafter called “DMD”) having several hundreds of thousands of mirror elements, each of which can be controlled in inclination, on a semiconductor memory cell, and controls the inclination of each mirror element to control a reflecting condition to form an image. As illustrated in FIG. 1, in this DMD projector, light emitted from light source 101 is reflected by reflecting mirror 102, and converged by condenser lens 103 to a point on color wheel 110 which is provided with red (R), green (G), and blue (B) filters (hereinafter sometimes called “RGB filters”) in a spiral pattern to selectively allows each of red, green blue color to pass therethrough. The light which has passed through color wheel 110 is uniformalized by light waveguide (hereinafter called “integrator rod”) 104, transformed into collimated light flux by relay lens 105, and irradiated to DMD 107 through total internal reflection prism (hereinafter called “TIR prism”) 106. The light irradiated to DMD 107 is reflected therefrom in accordance with an image signal applied to DMD 107. The reflected light, i.e., image light which is modulated light, again passes through TIR prism 106, and is projected onto a screen through a projection lens 108 which has a zooming function.
Such a DMD projector is called a “Field Sequential Color system” (hereinafter called “FSC system”). There is a Sequential Color Recapturer system (hereinafter called “SCR system”) which is capable of improving the light utilization efficiency by approximately 40% higher than the FSC system. As illustrated in FIG. 2, the SCR system is provided with an integrator rod having both ends that serve as quasi reflection planes. Light emitted from light source 201 is reflected by reflecting mirror 202, and is focussed on an incident end face of integrator rod 204 by condenser lens 203. The light traveling through integrator rod 204 exits from an emission end face, and impinges on color wheel 210. Part of the light incident on color wheel 210 at certain wavelength is transformed into collimated light flux by relay lens 205, and is irradiated to DMD panel 207 through TIR prism 206. However, another part of the light is reflected by color wheel 210, and again impinges on integrator rod 204 from the emission end face. The light, which has impinged again, travels through integrator rod 204 up to the incident end face, is reflected again by the incident end face, emitted from the emission end face of integrator rod 204 together with the light from light source 201, and again impinges on color wheel 210. Subsequently, similar actions are repeated. In this way, the light is reflected between the incident end face of integrator rod 204 and color wheel 210 multiple times to enhance the light intensity. In addition, the resulting illumination light, which has a uniform brightness distribution, is irradiated to DMD 207 through TIR prism 206 and modulated as mentioned above. The light (projected light) modulated by DMD 207, which represents an image, is projected through TIR prism 206 and projection lens 208, thereby displaying the image on a screen or the like.
The SCR system has limitations in increasing the light utilization efficiency through repetitive reflections of light in integrator rod 204 due to a low reflection efficiency on the incident end face of integrator rod 204, and is expected to provide merely about 40% of improvement as compared with the FSC system as described above. To surpass the SCR system, there has been proposed techniques for improving the light utilization efficiency by modulating colored light of one color which is transmitted by an RGB filter of a color wheel and colored light of another color which is reflected by the RGB filter, respectively and projecting the resulting light. Japanese Patent Laid-Open Publication No. 228535/2001 and Japanese Patent Laid-Open Publication No. 264953/99 have proposed techniques for decomposing light reflected by a color wheel and light transmitted by the color wheel as different colored light components, applying each of the decomposed colored light components to a respective separate image display device to display an image, and superimposing the images of the respective colors within a projector or on a screen to project a color image. However, these techniques require a number of image display devices as much as the number of decomposed colored light components, and also require an optical system for synthesizing images of respective colors, thus suffering from a problem of a complicated structure.
On the other hand, Japanese Patent Laid-Open Publication No. 264689/2001 has proposed techniques for spatially decomposing light from a light source into RGB colored light components in a color filter, dividing a display surface of a single image display device into three areas, sequentially irradiating each of the divided areas with decomposed RGB colored light components to display images in the respective divided areas in time division. Japanese Patent Laid-Open Publication No. 264689/2001 also discloses techniques for increasing the light utilization efficiency by returning reflected light, which is provided when each colored light is transmitted by the color filter for separation, toward a light source to reuse the reflected light.
Japanese Patent Laid-Open Publication No. 264689/2001 is advantageous over Japanese Patent Laid-Open Publication No. 228535/2001 and Japanese Patent Laid-Open Publication No. 264953/99 in the ability to simplify the structure because RGB colored light components are sequentially irradiated to each of the divided areas on the image display device. However, Japanese Patent Laid-Open Publication No. 264689/2001 simply returns reflected light provided during the separation toward the light source, and since the reflected colored light is again reflected by the same color filter, it is difficult to increase the transmission efficiency of each colored light at the color filter. Consequently, Japanese Patent Laid-Open Publication No. 264689/2001 actually provides the light utilization efficiency substantially equal to that of the SCR system, and encounters difficulties in realizing an expected light utilization efficiency three times higher than that of the FSC system.